Poly(ADP-ribosyl)ation is a post-translational modification that plays a central role in the regulation of cell death and DNA repair. PAR serves as a surrogate marker for poly(ADP-ribose) polymerase (PARP) and poly(ADP-ribose) glycohydrolase (PARG), which are being actively pursued as therapeutic targets with several PARP inhibitors already in clinical trials. Central to understanding PAR regulation and PARP/PARG drug discovery would be the availability of sensitive, simple and low-cost assays, which are currently unavailable. Thus this Phase 1 application seeks to develop homogeneous assays for PAR utilizing engineered split-protein reporters. The new pharmacodynamic and cellular assays that are proposed will help advance treatment regimens as well as accelerate the development of PARP and PARG inhibitors in both academia and industry. PUBLIC HEALTH RELEVANCE: Poly (ADP-ribosylation), a post-translational modification of proteins, plays a central role in the repair of single strand breaks caused by environmental and metabolic stress. Poly(ADP-ribose) levels in cells are maintained by the dual action of PARP, which synthesizes PAR;and PARG, which degrades PAR in cells. Hence PAR can be used to report on the activity of both these enzymes. The purpose of our application is to develop low-cost, sensitive, luminescence based poly(ADP-ribose) detection assays for drug discovery.